Scale conversion device



United States Patent lnventor Appl. No.

Filed Patented Assignee Priority SCALE CONVERSION DEVICE 10 Claims, 4 Drawing Figs.

US. Cl. 1l6/ll5.5,

Int. Cl B23q 17/00 Beaumont J Davies Putnoe, England GeorgeRiehards & Company Limited Broadheath, Altrincham, Cheshire,

a company of Great Britain [50] FieldofSearchW: 116/115,

115.5, 133, 129; 74/10, 813, (lnquired); 33/166; 82/(1nquired) [56] References Cited UNITED STATES PATENTS Primary Examiner-Louis J. Capozi Attorney-Holcombe, Wetherill and Brisebois ABSTRACT: This invention is a device for fitting to machine tools enabling graduations in inches to be converted into graduations on the metric system by use of a belt which runs over the drum carrying the inch graduations as a pulley.

f I SCALE CONVERSION DEVICE The invention is concerned with -a device for converting measurements in one system of units to measurements in another system. Such a device may for example be used to enable a metric dial indicator to be obtained from a machine tool fitted with lead screws in which the pitches are measured in inches.

According to the present invention a device for converting measurements in a first system of units to measurements in a photographically applied from a master is 25 sprocket holes long (i.e. with a total length of belt representing 10 mm). The

sprocket holes may be punched in it before application of the markings. The belt 8 is nearly twice as long as the circumference of the cylinder 2 and the additional length is taken up second system consists of a cylinder carrying around it graduations each representing measurements in one system of units, the cylinder acting as a pulley for driving a belt carrying graduation representing corresponding measurements in the second system of units.

Preferably the belt is mounted on a sprocket on the cylinder to prevent slipping and to prevent cumulative errors in the belt length. The belt length is conveniently chosen to represent a whole number of units in the second system. This beltlength may be taken up by pulleys and one of them could be arranged to drive a decade counter. An optical reading device operating in conjunction 'with the belt and second scale can provide a decimal read out.

Such a device is inexpensive to produce and requires only a simple modification to a standard scale marked with the first system and is more trouble free at high speeds than devices for similar purposes which involve meshing gear wheels. Speeds representing a linear pitch movement of a lead screw of 2 inches per second have been satisfactorily achieved.

The invention may be carried into practice in various ways and one embodiment will now be described by way of example with reference to the accompanying drawing in which:

FIG. 1 is a sectional elevation of a conversion device applied to a lead screw of a machine tool;

FIG. 2 is a view of the device with the cover removed and showing the scales;

FIG. 3 is a section on the line III-III in FIG. l but with some components not shown; and

FIG. 4 is a plan view showing the appearance to a user.

A lead screw 1. having a pitch of 0.2 inches carries a calibrated cylinder 2 with a circumferential scale 3 having 200 divisions, with every tenth division bearing an identifying number. Thus the circumference of the cylinder will represent a linear movement of 0.2 inches, and each division .will be equivalent 'to 0.001 inches of movement by the lead screw. The lead screw position can be determined in inches by a fixed reference line 6, or possibly by a vernier device. The cylinder 2 has a large central hole which is useful for accommodating a great variety of standard shafts by use of suitable adapters 4. A handwheel 7 enables the lead screw 1 to be turned by hand.

The cylinder 2 also carries 127 sprocket teeth 5 for driving a belt 8, which also passes under the reference line 6.

The belt 8 for example of terylene ultrasonically welded from strip after numerals and scale divisions 9 have been bythree pulleys 10, from which a decade counter may be idriven if required. The pulleys are out away as shown except at each end, to save wear on the markings. The cylinder also i could be out away between the edges of the belt,

In some cases it may be satisfactory to omit teeth from some of the 127 positions on the drum. Theteeth left should be approximately evenly spaced. The belt and pulley system is j mounted in a. casing 11 with a transparent window 12 through which to view the scale, and a shutter 13 can be set over the window 12 to mark the 'scale 3 or 9 which is not being used. The window 12 can be mounted in any of the three positions shown in FIG. 3 as is most convenient for the particular machine.

The cylinder2 can be rotated and locked with respect to the lead screw 1 for datum setting.

I t In an alternative arrangement, the millimetre graduation I could be carried without identifying numerals on the cylinder 2, and the numerals could move with the belt to identify the .graduations in any position. This is very accurate because the graduations are on the same member, but the arrangement shown in the drawings does not produce cumulative errors ibecause of the sprocket drive and the manufacture is simiplified because all additional markings can be photographii cally. applied to the belt in the flat.

The device can be designed for lead screws of any pitch. For leadscrews with a pitch in the inch system, the sprocket contains 127 teeth or a multiple of 127 but the scale 9 may con,- tain any number of divisions, possibly 508, each representing 0.01 mm. The length of the. belt will be normally chosen to give a length representing an integral number of identical lengths representing for example 1 mm, 10 mm., or 100 mm. sections. The length is chosen togive the most convenient numbering.

The sprocket 5 prevents slipping of the belt and eliminates small cumulative errors in belt length, and the system is simple, cheaper, and more accurate than gearing for driving a millimetre cylinder from an inch cylinder.

For lead screws with a pitch in the metric system that require conversion to give a reading in inches, there would be 25, 50 or 100 sprocket teeth.

The following Tables 1 and 2 show examples of the design of the unit for inch and metric system screws respectively. The example in the specification is the second one in Table 1.

In Table 1, Y/X=Z/25.4A In Table 2, Y/X=25.4 Z/A those letters.

TABLE 1.-INCH TO METRIC Examples of possible arrangements No. of divs.

in metric scale it scale is on drum Lead screw pitch ins.

No. of divs. Each div. of No. of No. oil in metric metric scales teeth on sprocket scale it scale represents sprocket holes in is on bolt mm. and heel belt Bell; calibration X Y Z 300 01 127 150 0 to 1 mm. three times. 500 02 127 250 0 to 10 mm. 300 02 127 150 0 to 1 mm. six times. 200 05 127 200 0 to 10 mm. l 127 200 0 to 10 mm. two times.

TABLE 2.ME'IRIC TO lNCII Examples of possible arrangements Each div. of N0. of N o. of divs. inch scale No. of teeth sprocket Lead screw pitch, in inch scale represents on sprocket holes in Belt mm. on belt in. wheel bolt calibration X Y Z 500 0002 50 127 to 0.1 in. 500 0001 100 1.27 0 to 0.05 in. 250 002 50 127 0 to 0.5 in. 500 002 25 127 0 to 1.0 in. 250 001 100 127 0 to 0.25 in. 500 002 50 127 0 t0 1 in. 250 .002 100 127 0 to 0.5 in. 400 005 50 127 0 t0 2 in. 200 .005 100 127 0 to 1 in.

Note that in this case the inch scale should be on the belt.

I claim: 1. A device for converting measurements in a first system of units to measurements in a second system of units comprising a cylinder having a principal axis, and carrying on a circumferential surface thereof graduations representing measurements in one-system of units, mounting means on which said cylinder is mounted for rotation about said axis, belt driving means rotatable with said cylinder, a flexible belt carrying graduations representing corresponding measurements in the second system of units and driven by said driving means in a path encircling said cylinder, in the course of which path said belt passes over a part of said peripheral surface adjacent the graduations on said cylinder, and is constrained by said driving means to travel with said part of said cylinder surface as said cylinder turns.

2. A device as claimed in claim 1 in which driving means is a sprocket drive.

3. A device as claimed in claim 2 including sprocket teeth on the cylinder and sprocket holes in the belt.

4. A device as claimed in claim 1 in which the belt length is equivalent to a whole number of units of the second system.

5. A device as claimed in claim 1 including a system of pul- 6. A device as claimed in claim 1 including an optical arrangement enabling a measurement to be read on either system of units.

7. A device as claimed in claim 1 in which the ratio of the length of the belt to the circumference of the cylinder is equal to the ratio of the measurement on the second system corresponding to the full length of the belt to the measurement on the first system corresponding to the circumference of the cylinder, multiplied by a factor relating the two systems of units.

8. A device as claimed in claim 1 in which the cylinder also carries graduations in the second system of units while the belt carries markings for identifying these graduations.

9. A device as claimed in claim 1 which the belt carries I graduations in the second system of units and markings identifying them.

10. A device as claimed in claim 1 including a lead screw of a machine tool the pitch of which is indicated by the graduations in the first system of units on the whole circumference of the cylinder, the cylinder being mounted on the lead screw. 

